Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$58.43	13.712%	$66.4419	$66.44	$66.45	$66.40
Purchase #2	$233.93	3.727%	$242.6486	$242.65	$242.65	$242.60
Purchase #3	$31.90	11.391%	$35.5337	$35.53	$35.55	$35.50
Purchase #4	$105.38	6.697%	$112.4373	$112.44	$112.45	$112.40
Purchase #5	$38.79	3.788%	$40.2594	$40.26	$40.25	$40.30
Purchase #6	$82.43	11.638%	$92.0232	$92.02	$92.00	$92.00
Purchase #7	$146.82	9.179%	$160.2966	$160.30	$160.30	$160.30
7 purchase totals =	$697.68		$749.6407	$749.64	$749.65	$749.50